The lighting unit according to the invention is intended to be used in lighting applications, i.e. provide a light output suitable in particular for illumination purposes. Particularly, but not exclusively, a lighting unit according to the invention may be used as an LED replacement for prior art lamps, such as incandescent or fluorescent lamps (LED retrofit). For this use, the lighting unit needs to be provided with mechanical and/or electrical means compatible with the lamp to be replaced.
LEDs (Light Emitting Diodes) offer advantages such as high efficiency and long lifetime. However, an individual LED delivers luminous flux only from a small area. For lighting purposes, generally a plurality of LEDs are required.
US 2008/0290814 A1 discloses a light emitting diode (LED) lamp mounted to an existing fixture for a fluorescent lamp. The fixture comprises a ballast delivering electrical power to the lamp, which has a tubular housing around discrete or surface mount LEDs compactly arranged and fixedly mounted on a flat rectangular flexible circuit board. The AC power generated by the external fluorescent ballast is converted to DC power by bridge rectifiers to convert the AC voltage to DC voltage. The individual LEDs may be electrically connected in series, in parallel, or in a combination of series and/or parallel configurations. In preferred examples, two LEDs are connected in series with a current limiting resistor. A plurality of such series circuits are connected in parallel to the rectifier. A filter capacitor may be also arranged in parallel.
A lighting unit as described in US 2008/0290814 A1 may be used for retrofitting, i.e. replacing prior art fluorescent lamps by a lamp, or lighting unit, based on LEDs. However, the electrical design is not flexible, so that for a different number of LEDs the electrical circuitry needs to be adapted.